fix: enable CJS interop and splitting

- This lets CJS users avoid .default.  The downside is the CJS and ESM types are slightly different: ESM exports as default, while CJS exports as module.exports =.  Hopefully that misalignment doesn't matter...

Author: JasonWeinzierl

tsup.config.ts

@@ -6,5 +6,7 @@ export default defineConfig({
   ],
   clean: true,
   dts: true,
+  cjsInterop: true,
+  splitting: true,
   format: ['cjs', 'esm'],
 });